Electrolytic production of unsymmetrical dimethylhydrazine



United tates Patent ELECTROLYTIC PRODUCTION OF UNSYMIVIETRI- CAL DIMETHYLHYDRAZINE David Horvitz, Landover, Md., and Edward Cerwonka, Carbondale, Pa., assignors to National Distillers and Chemical Corporation, a corporation of Virginia No Drawing. Application September 10, 1956 Serial No. 610,440

10 Claims. (Cl. 204-74) The present invention relates to a method for preparation of unsymmetrical dimethylhydrazine by electrolytic reduction of nitrosodimethylamine. f the various methods known to those skilled in the art for preparation of unsymmetrical dimethylhydrazine, hereinafter referred to as UDMH, one of the better methods involves the synthesis of N-nitroso-dimethylamine which is subsequently reduced by the action of Zinc dust in acetic acid to yield the desired product. However, and particularly due to the costly reagents employed for the reduction operation, such an operation is very expensive whereby it is highly desired that a process be provided that not only is capable of producing UDMH in high yields but also in a more economical manner than heretofore employed processes.

The present invention is based on the discovery that N- nitrosodimethylamine in aqueous solution can be subjected to electrolytic reduction to produce UDMH and, especially by use of certain conditions, the reduction can be carried out at relatively high current efiiciencies with obtainment of yields of at least about 90% UDMH.

In carrying out the electrolytic reduction process embodied herein, it may be performed in a neutral electrolyte but, preferably, in an acid solution with a preferred solution containing a ratio of about one mole of an acid (e.g., sulfuric acid) per mole of the nitrosodimethylamine subjected to electrolytic reduction. It is further preferred to employ as a catholyte solution an aqueous acid solution containing a molar ratio of acid to nitrosodimethylamine of from about twenty moles of acid per mole of nitrosodimethylamine to about one mole of acid per mole of nitrosodimethylamine. When such an acid solution is employed, all of the acid need not be added at the start of the process in which case only a part of the acid is added initially followed by further addition or additions of acid as the reaction proceeds to reduce the nitrosodimethylamine to UDMH.

Another condition which affects the yield of UDMH 5171 current efficiency in the process embodied herein is the concentration of nitrosodimethylamine in the solution. When the solution is very dilute, it has been found that the current efficiency is relatively low although high yields of UDMH are obtained whereas, at higher concentrations, both yields of UDMH and current efficiencies are markedly improved. For example, both yields of UDMH and current efiiciencies are improved as the concentration of nitrosodimethylamine is increased up to about 0.5 mole per 150 ml. of water. Use of concentrations of nitrosodimethylamine in higher concentrations generally results in a decrease in yield of UDMH. The concentration of UDMl-l that is produced does not appear to affect the yield of UDMH or current density in a critical manner whereby, in carrying out the reduction process, it is possible to add nitrosodimethylamine during the course of the reduction such as to maintain the concentration thereof at an optimum level but which does not exceed about 0.5 mole per 150 ml. of water while the UDMH 2 produced is continuously increasing in concentration. At optimum concentrations, the process embodied herein can be carried out with current efiiciencies of almost 100% with obtainment of UDMH in yields on the order of about 89 to about 92%.

The reduction process can be carried out with use of current densities that may be varied over a rather wide range as, for example, from about 0.023 ampere/cm. to about 0.24 ampere/cm. with obtainment of relatively high yields of UDMH. Optimum results are, however, obtained with use of a current density on the order of about 0.12 ampere/cm. although the optimum current density may vary somewhat depending on the particular concentration of nitrosodimethylamine that is employed. It is desirable, in carrying out the electrolytic reduction process, to employ. an electrolytic cell in which the catholyte is separated from the anolyte by suitable means such as a porous membrane. The reduction reaction occurs in the catholyte in which a cathode of suitable surface area and configuration is immersed. For such usage, the cathode may consist of mercury, lead, graphite or other suitable non-reactive conducting material. Particularly suitable results are obtained by use of lead cathodes and lead anodes.

As the anolyte, use is preferred of a conducting solution of acid concentration similar to that of the catholyte and, in the use of sulfuric acid, to an acid concentration on the order of about one mole of acid per mole of nitrosodimethylamine, so as to avoid diffusion of components between the catholytic and anolytic compartments. As heat is generated during the course of the electrolytic reduction, it is desirable to cool both the anolyte and catholyte by suitable means, as by water-cooled coils inserted in the liquids in the compartments. Although ambient temperatures are suitable and preferred for such a reduction operation, a temperature of from about 0 to about C. can also be employed.

Electrolytes other than sulfuric acid may be employed both in the catholyte and anolyte and, for example, materials such as sodium sulfate, acetic acid, ammonium chloride, hydrochloric acid, and the like. However, use of sulfuric acid is preferred because of its low cost, its high conductivity and stability, and its excellent performances in a process as embodied herein.

The electrolytic reduction process is such that it may be carried out in a continuous as well as a batch operation. In operations in continuous manner, material from the catholyte is continuously withdrawn as fresh solution of nitrosodimethylamine and sulfuric acid in water is added in appropriate concentration.

The isolation of the UDMH as a free base may be carried out in any of several ways and, for example, by neutralization of the acid solution with a substance such as calcium hydroxide, calcium oxide, etc. to produce a precipitate of the calcium salt (e.g., calcium sulfate) which is filtered off. From the resulting solution, the UDMH can be recovered by fractional distillation. However, in the use of such materials (calcium oxide, calcium hydroxide) for neutralization, such a large mass of the salt of calcium (e.g., calcium sulfate) is produced that it is very diflicult to obtain substantially complete recovery of the UDMH by washing the large mass of solid. On the other hand, it has been found that by use of calcium oxide (e.g., powdered) in an amount sufilcient to effect a substantial but only partial neutralization (e.g., about 80%), followed by completion of the neutralization with sodium hydroxide, a filterable solid is formed from which a high recovery of UDMH can be obtained.

In order to further describe the invention the following embodiments are set forth for purposes of illustra- Hull and not limitation. I

Example 1 A solution containing 1,372 gm. (14 moles) of sulfuric acid in 1,050 ml. of water was prepared. The total volume measured 1,722 ml. of which (246 ml.) was placed in a porous cup which served as the cathode compartment. The remainder of the solution was placed in the anode compartment. To the catholyte was added 37 gm. (0.5 mole) of nitrosodimethylamine. A stirrer was employed to agitate the catholyte and a cold-finger condenser was immersed in it to keep it at ambient temperature. A current of 20 amperes was permitted to flow through the cell which for the surface area of cathode (lead) employed gave a current density of 0.12 ampere/cmfi. At the end of one hour, a 1 ml. sample was removed and analyzed for unsymmetrical dimethylhydrazine. It was found that the rate of production of unsymmetrical dimethylhydrazine was 0.209 mole per hour. An additional 0.2 mole (14.8 gm.) nitrosodimethylamine was added at the end of each hour until a total of 2.0 moles had been introduced. Since four equivalents of hydrogen are required to reduce a mole of the nitroso compound to unsymmetrical dimethylhydrazine, the theoretical current requirement of the reaction is 107.2 ampere-hours per mole. With a current flow of 20 amperes, the theoretical time required for the reduction of 2 moles is therefore 10.72 hours. The reaction described above was found to be complete after 11 hours, since samples assayed after that time showed no increase in yield of unsymmetrical dimethylhydrazine. The yield obtained in this case was 83.7%, based on the weight of nitroso compound.

Example 2 A catholyte containing the following ingredients was prepared: Nitrosodimethylamine, 37 gm. (0.5 mole), concentrated sulfuric acid, 80 ml. (1.5 moles), and water 150 ml. The anolyte comprised a solution of 480 ml. sulfuric acid in 900 ml. of water. The electrodes consisted of a lead rod anode and lead plate anode. The area of the lead cathode was such that a current density of 0.12 ampere/cm. was obtained. A current of 20 amperes was passed through the cell for a period of 3% hours. The yield at the end of 3 hours was 92.4% dimethylhydrazine, based on nitrosodimethylamine and it did not appreciably increase in the last half hour.

Example 3 Solutions were prepared of the same concentration as described in Example 2 above, except that 7.4 gm. of nitrosodimethylamine (0.1 mole) were used. A pair of graphite rods were used as electrodes in this experiment. The current density employed was 0.167 ampere/cm. At the end of 1 hour, the yield of dimethylhydrazine was found to be 77% and did not appreciably increase after further passage of current.

Example 4 In this experiment the catholyte solution consisted of 37 gm. of nitrosodimethylamine (0.5 mole), and 54 ml. of concentrated sulfuric acid (1 mole), dissolved in 150 ml. of water. The anolyte consisted of 319 ml. of concentrated sulfuric acid dissolved in 900 ml. of water. An additional 37 gm. of nitrosodimethylamine were added to the catholyte during a period of 3 hours while the electrolytic reduction was in progress. Two lead electrodes were used in this experiment. A current density of 0.12 ampere/cm. was employed. The yield obtained was 89% at the end of the theoretical time. The temperature was permitted to reach 40 C. during the course of the electrolysis.

Example 5 A catholyte solution was prepared which consisted of nitrosodimethylamine 7.4 gm. (0.1 mole), dissolved in 1,690 ml. of an 8% sodium sulfate solution. The anolyte consisted of 247 ml. of 8% sodium sulfate solution. A lead rod was used as anode and a pool of mercury comprised the cathode. The current density was 0.045 ampere/cm. The yield of dimethylhydrazine was 10.8% at the end of 1 /2 hours.

Example 6 Percent 2 hours 50 3 hours S7 3 hours 45 minutes 62% 4 hours 20 minutes 64 5 hours 64 Example 7 A 10% ammonium chloride solution was prepared, of which 250 ml. were used for the catholyte of the cell, and 1500 ml. for the anolyte. To the catholyte was added 0.1 mole (7.4 gm.) of nitrosodimethylamine. The current density was 0.12 ampere/cmf At the end of 1 hour the yield of unsymmetrical dimethylhydrazine was 14.1%.

Example 8 The following results were obtained when electrolytic reductions were performed with solutions and conditions kept constant, only the current density being varied. The solutions used contained 0.3 mole of nitrosodimethylamine and 0.3 mole of sulfuric acid in 1 liter of water.

Percent Yield of Unsymrnetrlcal Dimethvlhydrazine Current Density (ampereslcm While there are above disclosed but a limited number of embodiments of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claims as are stated therein.

What is claimed is:

1. A process for production of unsymmetrical dimethylhydrazine which comprises electrolytically reducing N- nitrosodimethylamine in an aqueous acid solution wherein the catholyte solution contains a molar ratio of acid to nitrosodimethylamine of from about twenty moles of acid per mole of nitrosodimethylamine to about one mole of acid per mole of nitrosodimethylamine.

2. A process, as defined in claim 1, wherein the electrolytical reduction of the amine is carried out in an aqueous acid solution containing sulfuric acid.

3. A process for production of unsymmetrical dimethylhydrazine which comprises electrolytically reducing N-nitrosodimethylamine in an aqueous acid solution containing a ratio of one mole of acid per mole of the nitrosodimethylamine.

4. A process for production of unsymmetrical dimethylhydrazine which comprises electrolytically reducing nitrosodimethylamine in aqueous solution containing up to about 0.5 mole of the nitrosodimethylamine per ml. of water.

5. A process for production of unsymmetrical dimethylhydrazine which comprises electrolytically reducing nitrosodimethylamine in aqueous solution at a current density of from about 0.023 to about 0.24 ampere per cm.

6. A process for production of unsymmetrical dimethylhydrazine which comprises electrolytically reducing N- nitrosodimethylamine in an aqueous acidic solution containing a ratio of one mole of sulfuric acid per mole of the nitrosodimethylamine and up to about 0.5 mole of the nitrosodimethylamine per 150 ml. of water, said electrolytical reduction being carried out at a current density of from about 0.023 to about 0.24 ampere/cm? 7. A process, a defined in claim 6, in which the electrolytic reduction is carried out at a temperature of about 0 to about 80 C.

8. A process, as defined in claim 6, wherein the electrolytic reduction is carried out at a current density of about 0.12 ampere/ch11 9. A process, as defined in claim 6, wherein the unsymmetrical dimethylhydrazine in the acid solution from the electrolytic reduction of the nitrosodimethylamine is isolated by neutralizing the acid solution and fractionally distilling the unsymmetrical dimethylhydrazine from the neutralized solution.

10. A process, as defined in claim 9, wherein neutrali zation of the acid solution is carried out by partially neutralizing with calcium oxide followed by completion of the neutralization with sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS McMillan Oct. 25, 1949 Smith et al. Mar. 18, 1952 OTHER REFERENCES Electro-Organic Chemistry by C. I. Brockman, John Wiley & Sons, New York (1926), pages 263, 264.

Wells et al.: J. Am. Chem. Soc. 58, pages 2630 2632 (1936).

Chemical Abstracts (1933), vol. 27, page 23 6 Electrolytic Preparation of Hydrazines.

Swann, Jr.: Transactions of the Electrochemical Society, vol. 77 (1940), page 482.

Backer: Recuel des travaux chemique des Pays-has, vol. 31, pages 142, 143, 152; vol. 32, pages 39-47. 

